The use of a scanned gas-cluster ion beam (GCIB) processing a surface of a workpiece, for etching, cleaning, and smoothing surfaces is becoming a well-established industrial process. Scanned ion beams are also used in the field of ion implantation where conventional monomer ion beams are used rather than GCIBs. In most equipment that uses scanned ion beams to uniformly process a surface of a workpiece, there is a problem that results when undesired arcs occur at high voltage points in the equipment. In most circumstances, the occurrence of a high voltage arc in an ion-beam processing tool results in a momentary interruption of the ion beam. In a beam-scanning or workpiece-scanning system, by the time the arc has been extinguished, scanning has often moved the ion beam relative to the workpiece so that normal processing resumes at a different position on the workpiece than where it was terminated by the arc. The normal result is that a portion of the workpiece is not uniformly processed, and this often results in a reduced product yield in the ion beam processing equipment.
A high voltage power supply normally has a stored energy that can be discharged rapidly by an undesired arc, but which may not be rapidly recovered. Also, regulation circuits may not respond quickly when an arc discharges a high voltage power supply. For these and for other reasons, it is often the case that when a high voltage power supply is discharged by and undesired arc, normal operating voltage may not be restored for a period of tens or even hundreds of milliseconds (msec.) In high throughput processing equipment like an ion implanter or a GCIB processor, such a lengthy recovery time results in non-uniformity of the process.
Another problem arises when an undesired arc rapidly discharges the high stored energy of a high voltage power supply, Electromagnetic Interference (EMI) transients can disrupt the operation of control systems, or even destroy sensitive components in nearby electronic circuits. For this reason it is highly desirable, in the event of an unintended high-voltage arc, that the arc be interrupted before the entire stored energy of the high voltage power supply is dumped.
Accordingly, it is an objective of the present invention to provide a fast responding means to terminate an unintended arc so that normal processing can be rapidly restored.
A further objective of the invention is to provide an electrically floating apparatus for terminating an unintended high voltage arc at a high voltage terminal without need of a separate power source nor any other connection to the ground terminal of a high voltage power source. Another objective of the present invention is to provide a means to terminate an intended high voltage arc without permitting the complete discharge of stored energy in the high voltage power source.